it is inferred that
their life is life in its lowest degree. But inanimate bodies are
inferior to plants. Therefore they have not life.

_I answer that,_ We can gather to what things life belongs, and to what
it does not, from such things as manifestly possess life. Now life
manifestly belongs to animals, for it said in _De Vegetab._ i [*De
Plantis i, 1] that in animals life is manifest. We must, therefore,
distinguish living from lifeless things, by comparing them to that by
reason of which animals are said to live: and this it is in which life
is manifested first and remains last. We say then that an animal
begins to live when it begins to move of itself: and as long as such
movement appears in it, so long as it is considered to be alive. When
it no longer has any movement of itself, but is only moved by another
power, then its life is said to fail, and the animal to be dead.
Whereby it is clear that those things are properly called living that
move themselves by some kind of movement, whether it be movement
properly so called, as the act of an imperfect being, i.e. of a thing
in potentiality, is called movement; or movement in a more general
sense, as when said of the act of a perfect thing, as understanding
and feeling are called movement. Accordingly all things are said to be
alive that determine themselves to movement or operation of any kind:
whereas those things that cannot by their nature do so, cannot be
called living, unless by a similitude.

Reply Obj. 1: These words of the Philosopher may be understood either
of the first movement, namely, that of the celestial bodies, or of
the movement in its general sense. In either way is movement called
the life, as it were, of natural bodies, speaking by a similitude,
and not attributing it to them as their property. The movement of the
heavens is in the universe of corporeal natures as the movement of
the heart, whereby life is preserved, is in animals. Similarly also
every natural movement in respect to natural things has a certain
similitude to the operations of life. Hence, if the whole corporeal
universe were one animal, so that its movement came from an
"intrinsic moving force," as some in fact have held, in that case
movement would really be the life of all natural bodies.

Reply Obj. 2: To bodies, whether heavy or light, movement does not
belong, except in so far as they are displaced from their natural
conditions, and are out of their proper place; for wh